Alan Judge volleyed home to give the Bees a half-time lead and central defender James Tarkowski nodded in a free-kick midway through the second half to seal matters.
To reach the play-offs, Brentford need to defeat Wigan at Griffin Park next Saturday and hope the Ipswich or Derby results go in their favour.
Brentford sat in fifth place and within the play-off positions at the start of the month, but a poor run of four matches without a win had left them in seventh and three points off the pace.
They had at least secured three draws in their winless sequence and made a vibrant start at the Madejski Stadium, going in front in the seventh minute after good work by Andre Gray.
Brentford’s top scorer, with 16 goals this season, jockeyed for position on the right flank before clipping over a superb cross to the near post. Judge timed his run perfectly to volley past home goalkeeper Adam Federici.
Reading, beaten FA Cup semi-finalists last weekend, had already scorned two chances. Garath McCleary tested Brentford goalkeeper David Button from 20 yards and Nathaniel Chalobah drove wide when well placed.
They produced more of the same after going behind. A header from Chalobah drifted harmlessly wide and McCleary blazed over after Hal Robson-Kanu’s miscued effort from a Chris Gunter cross.
Brentford were content to sit on their lead, allowing Reading to press forward almost at will. Chalobah drove over from a McCleary corner and Jamie Mackie cut inside only to shoot well off target.
Reading, without a goal in three league matches, kept pushing but, on a rare Brentford attack, Gray could have doubled the lead. His 20-yard shot was well struck but took a deflection behind for a corner.
McCleary responded for Reading with an attempt from long range that was blocked. At the other end, an Alex Pritchard drive was deflected wide.
Brentford survived comfortably until the interval and should have stretched their advantage soon after the restart. Gray raced through alone but, as he cut in from the angle and shot, Federici saved with an outstretched leg.
Reading responded brightly and Chalobah netted after Robson-Kanu’s close-range effort had been superbly saved by Button, but it was ruled offside.
It was a fortunate escape for Brentford, but they made the most of it by making it 2-0 in the 65th minute.
McCleary committed a clumsy foul on Jota, for which he was booked, and, from Judge’s nicely flighted free-kick, centre-back Tarkowski rose unchallenged to head past Federici.
Reading should have reduced the gap when substitute Simon Cox bore down on goal but he shot straight at Button.
Brentford held on easily at the end, with substitute Jon Toral almost making it 3-0 when his low drive struck a post.